Hydrostatic transmission



Nov. 15, 1966 R..J. LEASE HYDROSTATIC TRANSMISSION original Filed Marcha, 1965 2 Sheets-Sheet 1 NNN Nov. 15, 1966 R. J. LEASE HYDRUSTATICTRANSMISSION original Filed Maron s, 1965 2 Sheets-Sheet 2 United StatesPatent O 3,284,999 HYDROSTATIC TRANSMISSION Robert I. Lease, La Salle,Ill., assignor to Sundstrand Corporation, a corporation of IllinoisContinuation of application Ser. No. 437,652, Mar. 8, 1965. Thisapplication Feb. 1, 1966, Ser. No. 533,742 3 Claims. (Cl. 60-19) Thisinvention is a continuation of my application Serial No. 437,652, filedMarch 8, 1965, now abandoned (which is a continuation-impart of myapplication Serial No. 356,610, now abandoned) and relate-s tohydrostatic transmissions and more particularly to an improved controlmeans therefore.

Hydrostatic transmissions have found a great deal of use in tractor-typevehicles for propelling the vehicle. If the vehicle is encounteringditlicult terrain or heavy work load, the engine may begin to lose speedand approach stalling. It may be desirable to maintain a constant enginespeed to maintain a constant horsepower output at the transmission andtherefore means may be provided responsive to the engine speed foraccelerating the same in response to decrease thereof. However, if theengine is still incapable of maintaining speed under the load conditionsand continues to drop in speed further and more closely approachesstalling, then it is desirable to provide a second regulating orgovernor means which will Vary the power output of the transmission inresponse to a given drop of engine speed below that -for actuating theengine governor.

It -is therefore a primary object of this invention to provide a new andimproved control means for a hydrostatic transmission.

It is a primary object of this invention to provide a new and improvedcontrol means for a hydrostatic transmission which possesses theadvantages mentioned above.

It is another object of this Iinvention to provide a new and improvedcontrol means for a hydrostatic transmission having means responsive toengine speed for bringing an engine up to speed in response to a dropthereof while maintaining the power output of the transmission at aconstant level.

It is still another object of this invention to provide a new andimproved control means for a hydrostatic transmission having meansresponsive Ito the engine speed for bringing an engine up to speed inresponse to a drop in the output thereof while maintaining thetransmission output at a constant power and being further provided witha means for reducing the power output of the transmission in response toa further drop in engine speed below a predetermined level.

It is yet another object of this invention to provide a new and improvedcontrol means for a hydrostatic transmission having an engine governormeans responsive to a drop in engine speed to bring the engine up tospeed while maintaining the transmission at a constant power output, andhaving transmission governor means for varying the torque of thetransmission in response to a further drop in engine speed and beingfurther provided with means for selectively establishing an initialsetting for the activation of both the engine governor means andtransmission governor means.

Other objects, features and advantages of the present invention will beapparent from the following description of the preferred embodimentillustrated in the accompanying drawings, in which:

FIGURE 1 is a diagrammatic illustration of the control means of thisinvention; and

3,284,999 Patented Nov. 15, 1966 ice FIGURE 2 is a diagrammaticillustration of a hydrostatic transmission embodying the control meansof this invention.

Referring now to the drawings, in FIGURE 2, there is shown a hydrostatictransmission 10 having a closed hydraulic circuit 12 with an enginedriven pump 14 and a fluid driven motor 16. The pump is driven by anengine diagrammatically illustrated at 18 (FIGURE l) through suitablemeans diagrammatically illustrated at 19. In turn, the output of thetransmission is applied to an output shaft schematically illustrated at19a for appropriately propelling the vehicle. The closed circuit 12consists of conduits 21 and 22 which carry the pumped iiuid from thepump to the motor and return the same to the pump, with the pump outletconnected to the motor inlet and the motor inlet connected to the pumpoutlet in a Well known manner.

In the embodiment shown, both the pump and the motor are of an axialpiston type having rotatable cylinder blocks 14a and 16a, respectively,each with a plurality of cylinders in annular array and reciprocalpistons 14b and 161; therein. The pump has a reversible variable pumpswash plate diagrammatically illustrated at 24 which is engaged by thepistons 14b and the motor has a variable displacement motor swash platediagrammatically illustrated at 26 which is engaged by the pistons 16b.The combination of the fully reversible variable displacement pump swashplate and variable displacement motor swash plate gives the transmissionextreme flexibility so that it is capable of operating the vehicle ineither direction over a wide range of torque and speed therebypermitting an innite number of torque-speed output c-ombinations.

Operatively associated with the pump swash plate are the Apump controlcylinders 28 and 30 which are well known piston and cylinder devices andare connected to the -swash plate by the rods 28a and 30a forpositioning the swash plate in response to actuation by the cylinder.When the transmission is at neutral, the control cylinders maintain thepump swash plate in an upright position through the influence ofcenter-ing springs in each cylinder (not shown).

Similarly, the motor swash plate has operatively associated therewithmotor control cylinders 36 and 38 which are also well known piston andcylinder devices connected to the swash plate by rods 36a and 38a.

A control handle 46 is provided for selective actuation of thetransmission. In particular, the control handle 40 is mounted on a cam42 having pump cam slot 42a and motor cam slot 421) therein. A pumpcontrol pin 44 and motor ycontrol pin 46 are positioned in the slots 42aand 42b, respectively, and secured to the end of pump control link 44aand motor control link 46a, respectively, so that when the cam 42 isturned, the links will be appropriately moved. Links 44a and 46a areconnected through override springs 45 and 47 to move links 44h and 46h,respectively. By means of cross links 48 and 50 centrally pivotallymounted to the stems of a pump control valve 52 and motor control valve54, respectively, the pump control link 44b and motor control link 46bare operatively associated with the pump control valve 52 and motorcontrol valve 54, respectively.

The Aoverride springs 45 and 47 provide a normally rigid resilientconnection between the links 44a, 46a and the control valves 52 and 54,respectively. Each of the springs is a pivotally mounted torsion springwhich permits relative movement between the associated links when one ofthe links is restrained from movement. An

override spring of this type is described in detail in the Hannapplication, Serial No. 362,257, tiled April 24, 1964, now Patent No.3,212,263, issued October 19, 1965, assigned to the same assignee of thepresent invention. Override springs 45 and 47 provide several functionsin the present system. Firstly, they prevent damage to the controlvalves 52 and 54 when handle 40 is rotated beyond the position requiredto move the valves to their limit positions. Secondly, override spring47 permits links 46a and 46b to yield when an override signal issupplied to valve 54 in a manner more fully described below. Movement ofthe aforementioned control links 44b and 4Gb in a 'given direction inresponse to movement of control handle 40 will so position the valves 52and 54 to cause :Huid to be supplied through conduit 52a or 52b and 54aor S4b, respectively, to one of the pump control cylinders and motorcontrol cylinders for appropriate positioning of the pump and motorswash plates. It is to be noted that both the linkages 48 and 50 aresuch that, as the swash plates are moved in response to a lluid signalsupplied by the Valve 52, the linkages will be moved to reposition thevalve stem and thereby provide a feedback si-gnal which will tend toterminate the supply of control fluid to the control cylinders when thecontr-ol cylinders have moved the swash plates to the desired position.

It should be noted that the cam slots 42a and 42h are formed to stagethe pump and motor so that in bringing the transmission up to speed fromneutral the pump is tirst moved from neutral into stroke while the motoris held at maximum displacement after which the pump is held at maximumdisplacement While the displacement of the motor is reduced.

The transmission is provided with a positive displacement gear typereplenishing and cooling pump 56 which is also driven Eby the engine 18.The replenishing and cooling pump is in communication with a reservoir58 through a supply conduit 60 for supplying replenishing and coolinglluid to the system as well as control lluid by means of the chargeconduit 61. From the replenishing pump 56, liuid is passed through afilter 62 and exits therefrom through conduit 64 where some of the fluidis directed by conduit 66 to a speed sensing means 68. The remainingduid continues to ilow through the conduit 64 and is fed .by means of aconduit 69 into the valve 52. Fluid is supplied through conduit 72 tothe motor control valve S4.

A pair of spring-biased check valves 70 and 70a are provided fordischarging the liuid from line 22 to the low pressure side of thetransmission through one check valve while pressure in the high pressureconduit :of 21 and 22 will maintain the other valve closed. Aspring-biased make-up relief valve 73 is in communication with theconduit 64 and serves to remove excess fluid pumped fby the control pumpand conduct the same to drain in the reservoir when the transmission isin neutral.

The transmission is further provided with a pair of high pressure reliefvalves 74 and 76 which are in communication with the conduits 20 and 22by means of the conduits 74a and 74b Iand 76a and 7Gb. The function ofthe high pressure relief valves is to prevent abnormally high pressurein circuit 12 by relieving the two main hydraulic lines 21 and 22 ofsur-ge pressure which may occur during rapid Aacceleratimi of abruptbraking. Oil from the high pressure conduit Will pass by means of theconduits 74h or 7Gb to appropriately move the valve stems of the valves74 or 76, respectivel f, and then feed out to the other side of thesystem by means of either the conduits 76a or 74a, respectively.

For establishing a circuit between the main line 20 or 22 that is at lowpressure and a low pressure relief valve 78, a shuttle valve 80 isprovided. The shuttle valve 80 is in communication with the conduits 20and 22 -by means of the conduits 82, 84 and 82a, 84a, respectively, andprovides a means for removing heated oil which has -been displaced bycooling oil supplied by replenishing pump 56. Fluid from the mainconduit that is at high pressure acts through either conduit 82 or 82ato appropriately position shuttle valve 80 so that uid from the conduit84a or 84, respectively, may be placed in communication with the reliefvalve 78 by means of' the conduit 86. From the relief valve 78, thefluid passes to drain.

A heat exchanger 88 is provided in communication with the drain conduitsand in the path of travel of the fluid as it is returned from drain tothe reservoir 58. A bypass means 90 is provided for bypassing the coolerif an excessive pressure drop occurs thereacross.

A bypass valve 91 is provided between conduits 21 and 22. This valve hasa stem 92 associated With the vehicle brake pedal shown at 96, so thatit is actuated thereby. The valve is normally centered by a spring 93 sothat lluid iiow between the line is blocked bythe land 94. A drain 9S isprovided for conducting leakage fluid to drain for return to reservoir58. As shown in the diagram, the valve is in its neutral or normalposition :and does not permit flow between the two main lines 21 and 22during normal operation. During braking conditions, pressure can rapidly increase in the high pressure one of lines 21 and 22 which issupplying pumped iluid to the motor and this buildup can becomeincreasingly disproportionate to the pressure in the other or lowpressure one of lines 21 and 22. As the :brake pedal is applied, thevalve stem 92 is moved to the right (as shown in FIGURE 2) establishingcommunication between the lines 21 and 22 and permitting iiuid to passtherebetween intermediate the pump and the motor so that the uidpressure between the lines may be maintained at relatively safe levels.This valve is provided in addition to the previously described bypassvalves as a means directly responsive to braking conditions formaintaining similar pressure values between the two conduits.

In FIGURE l, there tion of the governor is shown a diagrammaticillustrameans of this invention. An engine throttle control and governorsetting handle 100 is provided for controlling the speed of the engine18 as well as establishing'a desired governor setting tor an enginegovernor 101 and transmission governor 102. Transmission ygovernor 102includes speed sensing lmeans 68. The v handle is provided with linkage103 which is pivotally connected to arm 106 at 104. Link y106 isconnected to a fixed pivot support 108. At pivot 108, the handlemovement is subdivided into two outputs by the two linkage means, suchas 110, which is associated with the engine governor 101 and 112, whichis associated with the transmission governor 102.

Linkage means 110 includes an arm 113 pivotally connected at 114 to link11's which extends from pivot 114 to a pivotal connection 116 with lever117 pivotally mounted at 120. Arm 118 on lever 117 is pivotallyconnected at 121 to one end of link 119. The other end of link 119 ispivotally connected to a piston 126:1. Linkage means 112 includes an arm122 on lever 106 pivotally connected at 123 toa link 124 which extend-sto a pivotal connection with a transmission governor cam on lever 106The engine governor 101 includes a biased stem 126 and resilient means,such as compression spring 127, interposed intermediate the stem and thepiston 126a. The plunger 126 is associated through pivot 128 and arm 129with the engine throttle 130 so that movement of the handle may betranslated through the associated linkages and pivots to control theengine throttle 130 for setting a desired engine speed. The Vengine 18rotatably drives a ilyweight carrier 101a in the engine governor 101through suitable means schematically represented by 131. The rotarycarrier in the engine governor is provided with pivoted flyweights I132which are adapted to move out in well known lyweight fashion, and urgeplunger 126 against the spring 127 in response to engine speed.

The transmission governor 102 is a yweight activated valve having a stem133 slidably mounted therein. The stem 133 abuts a compression spring134 which, in turn, abuts a piston 135, which engages the cam 125. Theengine 18 drives the transmission governor through suitable meansschematically represented at 136 to rotate a carrier 102a for pivotediiyweights 13S and cause them to fan out in a well known manner and movethe valve stem 133 against the urging of spring 134 to push inopposition to piston 135.

As previously mentioned, control fluid is supplied to the speed sens-orportion 68 of transmission governor 102 by means of conduit 66. Aconduit 137 is in communication with the transmission governor and motorswash plate displacement valve 54 so that when the valve stem 133 ismoved to permit fluid to pass around the reduced portion thereof and outthe conduit 137, it will be supplied to the motor displacement controlvalve 54 to move the latter to supply uid to cylinder 36 to increase theangle of motor swash plate 26, increase the displacement of the motorand thereby increase the torque and reduce the speed thereof. As thevalve 54 moves in this manner override spring 47 yields permitting link46b to rnove With respect t-o link 46a which is then held by the cam 42.

In operation, as the handle 100 is moved to the left, as shown by thearrow A in FIGURE 1, the associated pivots and linkages will set theengine throttle spring 127 for the desired engine speed. This act ofpositioning the engine throttle also will urge the engine governorpiston 12611 to compress the engine governo-r spring 127 and set theforce required by the flyweights to pivot out in flyweight fashion whenthe engine drives the engine governor. Similarly, the cam 125 will berotated to force the transmission governor piston 135 against the spring134 to set the force required for the transmission governor flyweights137 to fan out as the engine rotates the engine governor. The higher theengine speed set on the engine throttle, the greater the force requiredto overcome the pressure of the governor springs 127 and 134. However,the springs 127 and 134 are designed so that as the engine speedincreases the yweights move out in opposition to the springs. Once theengine approximates the speed established by the spring 127, any furthermovement of yweights 132 tends to reduce the throttle setting and holdthe engine speed at the desired value. If the vehicle begins to loseengine speed due, for example, to heavy load conditions encounteredthereby, the flyweights 132 will, under the influence of the spring 127,be pushed back. This movement of the spring 127 will also move theplunger 126 in a direction which causes an increased setting to beplaced on the engine throttle and thereby overcome the decrease in speedsensed by the engine governor.

The transmission governor spring and engine governor spring are sorelated that less force is -required at any given speed setting for theflyweights to overcome the transmission governor spring than is requiredof the ily- Weights of the engine governor t-o overcome the springtherefor. Thus, the transmission governor will sense a reduction inengine speed at a lower speed than that sensed by the engine governor.Therefore, only after the engine .governor is incapable of bringing theengine back up to a predetermined speed, will the transmission governorsense an additional drop in engine speed and -respond thereto. The valvestem 133 will move to the left Irom the position shown in FXGURE lestablishing communication between the -control uid conduit 66 and thedisplacement control conduit 137. This will supply uid to motordisplacement control valve 54 and urge the valve stem thereof to theleft as shown in FIGURE 2. This will have the effect of appropriatelysupplying control fluid to the motor control cylinder 36 so as toreposition the swash plate 26 toward a position of maximum displacementto increase transmission torque and reduce the speed thereof and therebyprevent a further drop in engine speed and eliminate the possibility ofstalhng the engine.

-In operation, it will be understood that with the engine operating at apredetermined speed, any increased load on the vehicle results in apressure rise in the system and an increased horsepower load on theengine. Normally, the engine governor tries to maintain the engine speeddetermined by the spring setting in the engine governor. lf the enginegovernor cannot maintain engine speed and the latter keeps dropping, thetransmission governor senses the drop and then attempts to reduce theload on the engine to prevent its stalling. That is, the transmissiongovernor increases the torque at the motor and reduces the speed,reducing the system pressure and maintaining a constant horsepower loadon the engine. Thus, the maximum horsepower is obtained from the engineat all times, rather than allowing small overloads t0 stall the engine.

I claim:

1. In a drive system, a pump, means for varying the displacement of thepump, a motor, means for varying the displacement of the motor, conduitmeans connecting the pump outlet with the motor inlet and the motoroutlet with the pump inlet so that the pump delivers uid under pressureto drive the motor and the motor returns uid to the pump, manuallyoperable means connected for controlling the pump and motor displacementvarying means to increase the displacement of the pump while holding themotor near maximum displacement and then `reducing the displacement ofthe motor while holding the pump nea-r maximum displacement thereby tobring the transmission up to speed, an engine for driving the pumpincluding an engine throttle -for controlling engine speed, a rotaryengine governor responsive to engine speed and controlling the enginethrottle to maintain engine speed at a predetermined value includingmeans for adjusting the setting of the governor to vary saidpredetermined value, a rotary transmission governor responsive to enginespeed and operable to increase the displacement of the motor upon a dropin engine speed to a value below the set predetermined value includingmeans for adjusting the setting of the governor to vary said lower speedvalue and manually operable means controlling said adjusting means forsimultaneously varying the governor settings.

2. In a drive system, a pump, a motor, uid operable means for varyingthe displacement of the motor, conduit means connecting the pump outletwith the motor inlet so that the pump delivers uid under pressure todrive the motor, control valve means for selectively porting iluid tosaid uid operable means for varying the displacement of the motor,manually operable means for normally positioning said control valvemeans including normally rigid -resilient means adapted to yield under apredetermined force, an engine for driving the pump including an enginethrottle for controlling engine speed, a rotary engine governorresponsive to engine speed for controlling the engine throttle tomaintain a predetermined engine speed, and a second rotary governorresponsive to engine speed for increasing the displacement of the motorupon a drop in engine speed to value below said predetermined valueincluding a governor valve connected to port fluid to and position saidcontrol valve means to increase motor displacement, said governor valvebeing adapted to override said manually operable means when the enginespeed drops to said value below said predetermined value.

3. In a hydrostatic transmission, a pump, a motor, means for varyingythe displacement of the motor, conduit means connecting the pump outletwith the motor inlet and the motor outlet with the pump inlet so thatthe pump delivers fluid under pressure to drive the motor and the .motorreturns uid to the pump, manually operable means connected to thedisplacement varying means for selectv ing any desired motordisplacement, an engine for driving the pump including an enginethrottle for controlling engine speed, a rotary engine governorresponsive to engine speed and controlling the engine throttle tomaintain engine speed at a predetermined value, and means 4foroverriding the manually loperable means for `controlling motordisplacement including a rotary transmission governor responsive toengine speed and. operable to increase the displacement of t-he motorupon a drop in engine speed to a value below the set predeterminedvalue.

8 References Cited by the Examiner UNITED STATES PATENTS 2,500,580 3/1950 Segsworth 2,694,288 11/1954 Nubling 3,003,309 10/1961 Bowers3,167,907 2/ 1965 Kempson EDGAR W. GEOGHEGAN, Primary Examiner.

1. IN A DRIVE SYSTEM, A PUMP, MEANS FOR VARYING THE DISPLACEMENT OF THEPUMP, A MOTOR, MEANS CONNECTING THE DISPLACEMENT OF THE MOTOR, CONDUITMEANS CONNECTING THE PUMP OUTLET WITH THE MOTOR INLET AND THE MOTOROUTLET WITH THE PUMP INLET SO THAT THE PUMNP D ELIVERS FLUID UNDERPRESSURE TO DRIVE THE MOTOR AND THE MOTORS RETURNS FLUID TO THE PUMP,MANUALLY OPERABLE MEANS CONNECTED FOR CONTROLLING THE PUMP AND MOTORDISPLACEMENT VARYING MEANS TO INCREASE THE DISPLACEMENT OF THE PUMPWHILE HOLDING THE MOTOR NEAR MAXIMUM DISPLACEMENT AND THEN REDUCING THEDISPLACEMENT OF THE MOTOR WHILE HOLDING THE PUMP NEAR MAXIMUMDISPLACEMENT THEREBY TO BRING THE TRANSMISSION UP TO SPEED, AN ENGINEFOR DRIVING THE PUMP INCLUDING AN ENGINE THROTTLE FOR CONTROLLING ENGINESPEED, A ROTARY ENGINE GOVERNOR RESPONSIVE TO ENGINE SPEED ANDCONTROLLING THE ENGINE THROTTLE TO MAINTAIN ENGINE SPEED AT APREDETERMINED VALUE INCLUDING MEANS FOR ADJUSTING THE SETTING OF THEGOVERNOR TO VARY SAID PREDETERMINED VALUE, A ROTARY TRANSMISSIONGOVERNOR RESPONSIVE TO ENGINE SPEED AND OPERABLE TO INCREASE THEDISPLACEMENT OF THE MOTOR UPON A DROP IN ENGINE SPEED TO A VALUE BELOWTHE SET PREDETERMINED VALUE INCLUDING MEANS FOR ADJUSTING THE SETTING OFTHE GOVERNOR TO VARY SAID LOWER SPEED VALUE AND MANUALLY OPERABLE MEANSCONTROLLING SAID ADJUSTING MEANS FOR SIMULTANEOUSLY VARYING THE GOVERNORSETTINGS.